Virus Assembly and Release

In 2005, almost twenty years after the discovery of HCV as the major causative agent of non-A non-B hepatitis, the entire infectious cycle of the virus was recapitulated in cell culture for the first time. Our laboratory and others succeeded in developing the cell culture system by exploiting a unique genotype 2a patient isolate, Japanese fulminant hepatitis-1 (JFH-1), which both replicates to high levels and supports the release of infectious particles. The advent of the cell culture system has at last allowed authentic virus entry, assembly, and egress to be investigated.

Structural proteins make up the physical virion, and include core, E1, and E2. Through genetic analyses, we have shown that the HCV core protein is essential for infectious virus production and are continuing to map the determinants important for this activity. Nonstructural proteins are not part of the virus particle but we have shown that they can be required for infectivity. We found that both p7 and NS2 play essential roles early in HCV virion morphogenesis. The functions of these nonstructural proteins in infectious virus production may involve physical interactions with the structural proteins, as defective genomes with mutations in core can be rescued by adaptive changes in p7 and NS2. We have recently determined the X-ray crystal structure of the NS2 protease domain and found it to be a dimeric enzyme with each monomer contributing to two composite active sites. This protease domain is essential for the role of NS2 in infectious virus assembly, although the catalytic activity of the enzyme is not. An understanding of the mechanisms by which the structural and nonstructural proteins contribute to the formation of an infectious particle may allow the development of assembly inhibitors and possibly lead to the development of noninfectious particles for vaccines.